The described apparatus and method are generally suitable for working on any type of material, here especially tissue or bone, and thus are also usable in medical technology.
When working on materials, especially in medicine and here especially for working on tissue and bone, it is important to have information available about the local properties of the material that is to be worked. For example, in a so-called trepanation, the cranium is opened in order to be able to perform neurosurgical procedures, an osseus access to the interior of the cranium of a living organism, such as for example a human being, being created.
Thus it is the paramount goal to protect the very closely abutting hard meninges, the dura mater, to prevent any type of injury by the tool that is used, as injuries of the dura mater can lead to an extended time for the surgery and also the postoperative healing of the wound, as well as to an increased risk of infection. Beyond that, in the event of an injury of the dura mater, further complications (healing of the wound, mortality and increased treatment costs must be considered.
It is further known in the prior art that for access to the interior of the cranium, special drills are to be used that make several bores along a resection line. These bores can subsequently be connected by an additional instrument or tool, the so-called craniotome, in order to thus create a removable piece of bone. Usually, such a craniotome is a cutting instrument with, for example, a slightly conical cutter with which the cut is made.
It is known to provide the cutter at its drive side with an angled shoe, and to thereby at least theoretically separate it from the dura mater. This shoe serves to protect the dura mater in the area that is to be cut and ensures that the dura mater is continually pushed away from the bone and is thus pushed away from the cutter.
This functional mechanism is known to fail, for example typically in the event of local variations of thickness of the cranial bone, as well as in the case of an adhesion of the dura mater to the cranial bone. Then, tearing of the dura mater can occur in a section that is not visible, as a result of which a direct reaction to this type of damage to the dura mater is not possible, and the damage thus often continues up to the end of the cutting process. During a surgical procedure, such an injury is to be repaired in a targeted manner, for which often the required sutures or duraplastic in addition to a significant extension of the surgical procedure can also be associated with the danger of a liquid fistula and thus the risk of a postoperative infection with a significant increase of mortality, as well as increased costs.
After removing the bone cover, additional surgical steps can be performed and, subsequent to these procedures, the bone cover can, as a rule, be replaced to the extent it is not destroyed by the growth of a tumor, trauma or similar. The cutting technique described above thereby leads to a residual osseous gap, which is the result of a cutting defect because of the bore holes as well as the cutting kerf.
In other medical areas such as, for example, in the mouth, jaw or facial surgery, as well as spinal column surgery, comparable problems result with respect to the protection of the soft tissue.
The subject matter of the invention, i.e. the subsequently described apparatus, as well as the method is, however, not restricted to the use of working on material in medical application areas. The apparatus and method of the type described in the following can be used across the board, in order to be able to work on any type of material, for example, also for working on inanimate bodies, especially hollow forms or two-dimensional structures.
In addition, German patent application DE 101 17 403 [U.S. Pat. No. 7,346,417] also describes a method and an apparatus for controlling material abrasion or working on a material. It is described here how to manually regulate or control a tool depending on the geometry of a specified object volume and a specified object form that is to be obtained with respect to the material abrasion, here, especially the change and the performance of a cutting or drilling tool depending on the navigation coordinates and, for example, then when the targeted object form has been attained, to switch the tool off.
In this type of working of a material it is considered to be disadvantageous, however, when the performance of the tool that is used varies, because of this known method or the known apparatus, it being especially known in the case of cutting or cutting tools that a decrease in performance can under certain circumstances even lead all the way to stopping n a material that is to be worked on, i.e. arresting of the tool in the material. Especially in medical applications, as well as in general in any type of application of working on material, this represents a significant disadvantage, as, at the moment it stops, a tool of this type can get out of control. At best, such a previously known apparatus for working on material can only be used with sufficient safety in this type of processing, if it is based on a rotating operating principle such as, for example, drilling or cutting, not, however, by working by sawing.